Has anyone done Personalized URL's or Personalized Landing Pages with force.com sites?

I am looking to be able to create a personalized landing page for a customer such as below:
www.freecarwash.ca/JohnDoe

The customer would receive the PURL on a postcard in the mail. When they go to the URL it would be pre-populated with the customers specific data.

Basically it is a pre-populated web form on a personalized url. 

Does anyone have a working example I can show my developer? Or can it even be done?

Any help would be greatly appreciated.